The true natural history of Crohn’s Disease (CD), does not exist since almost no patients with CD remain untreated during their disease course, but it is possible to gain an impression of the natural course by examining studies published in the last decades.
Crohn’s disease is a life-long condition, with periods of relapse and remission. There is no known cure.
In adults, disease location remains fairly stable over time. However, repeated cycles of inflammation lead to a transition from non-stricturing, non-penetrating (B1) disease through to both stricturing (B2) and penetrating (B3) disease.
The single most affected segment of the gastrointestinal tract is the terminal ileum. The disease is located in more than 90% of cases in the three main sites: large bowel exclusively, isolated small bowel disease, and combined small and large bowel involvement. Approximately one-third of patients present with large bowel disease, one-third with ileocolonic disease and one-third with small bowel disease localization. Oesophageal, gastric and duodenal CD lesions occur in 1–4% of patients, most often in association with CD elsewhere in the gastrointestinal tract. Perianal disease is often seen in connection with concurrent recto-anal CD, but may occur as an initial lesion without apparent disease elsewhere in 2–5% of newly diagnosed patients.
Perianal fistulas: In population-based studies the occurrence of perianal fistulas varies between 21 and 23%. The cumulative frequency of fistula occurrence was 12% at 1 year, 21% at 10 years and 26% at 20 years. Presence varies according to disease location. Perianal fistulas have the highest frequency in patients with colonic disease involving the rectum followed by colonic disease with rectal sparing then ileocolonic disease.
Paediatric patients have more extensive distribution at presentation, and extension of disease during the first 2 years from diagnosis occurs in approximately one third of patients.
Extra-intestinal manifestations: CD is associated with a range of extra-intestinal manifestations (EIMs) that may be the initial presenting symptoms of CD. Up to 40% of patients with CD have at least one EIM. Some are related to active bowel inflammation.
Due to complications, 50% of patients require surgery within 10y. Only 20% avoid surgery during their lifetime. The chance of a second operation is 30-50% in the 10 y following the first operation.
Risk factors for CD recurrence after surgery include penetrating/fistulizing disease behaviour, young age, short duration of disease before first surgery and ileocolonic disease.
Cigarette smoking has been studied extensively and is found to be associated consistently with endoscopic, clinical and surgical CD recurrence. The risk for re-operation 5 and 10 years after the first surgery for CD is significantly higher in smokers compared with nonsmokers (36% versus 20% at 5 years and 70% versus 41% at 10 years).
It is uncertain whether there is an increased risk of colorectal cancer in patients with Crohn’s disease (the largest study to date, published in 2012 by Jess et al, reported no excess risk). However, patients with small intestinal CD disease may be at increased risk of small bowel adenocarcinoma.
Traditionally, colonoscopic surveillance is recommended for patient sub-groups. Fertility is reduced in patients with active but not inactive disease. The psychosocial burden of IBD is often under-estimated. Psychosocial therapies are commonly used.
Mortality in CD: It has been suggested that an increased mortality exists but with the increasing use of biologicals in the treatment of CD it will be interesting to see if future data on mortality show a decrease or even an increase in the mortality risk related to immunosuppression. Since biologicals at present seem to be able to induce mucosal healing, we might see a change in the prognosis of CD regarding surgery in the future, with the increasing use of biologics earlier in the disease course.